Health experts have warned that the US decision to roll out new Covid boosters without clinical testing on humans risks denting public trust and increasing hesitancy about vaccines.
The Joe Biden administration is using the bivalent boosters, which contain the original Covid strain and the genetic code of the Omicron sub-variants BA4 and BA5, to vaccinate more Americans against the virus.
It has bought 171mn doses of the BioNTech/Pfizer and Moderna boosters for $5bn and fast-tracked their authorisation before human trials are complete, hoping that they provide better protection against the dominant variants than existing Covid vaccines.
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